Heart rate and swimming activity as indicators of post-surgical recovery time of Atlantic salmon (Salmo salar)

Abstract

Background: Fish telemetry using electronic transmitter or data storage tags has become a common method for studying free-swimming fish both in the wild and in aquaculture. However, fish used in telemetry studies must be handled, anaesthetised and often subjected to surgical procedures to be equipped with tags, processes that will shift the fish from their normal physiological and behavioural states. In many projects, information is needed on when the fish has recovered after handling and tagging so that only the data recorded after the fish has fully recovered are used in analyses. We aimed to establish recovery times of adult Atlantic salmon (Salmo salar) after an intraperitoneal tagging procedure featuring handling, anaesthesia and surgery. Results: Based on ECG and accelerometer data collected with telemetry from nine individual Atlantic salmon during the first period after tagging, we found that heart rate was initially elevated in all fish, and that it took an average of ≈4 days and a maximum of 6 days for heart rate to return to an assumed baseline level. One activity tag showed no consistent decline in activity, and two others did not show strong evidence of complete recovery by the end of the experiment: baseline levels of the remaining tags were on average reached after ≈ 3.3 days. Conclusion: Our findings showed that the Atlantic salmon used in this study required an average of ≈ 4 days, with a maximum interval of 6 days, of recovery after tagging before tag data could be considered valid. Moreover, the differences between recovery times for heart rate and activity imply that recovery time recommendations should be developed based on a combination of indicators and not just on e.g. behavioural observations.

Tag use to monitor fish behaviour in aquaculture: a review of benefits, problems and solutions

“…Despite this, DSTs can still provide valuable information, for instance in the form of high-resolution data that may shed light on fish recovery after surgery. Heart rate DSTs have shown that the heart rate of tagged Atlantic salmon did not return to baseline levels for 4 days on average (up to 6 days) after surgery and anaesthesia (Føre et al 2020). This has implications for interpretation of data from transmitters or other electronic tags, as for salmon at least, the first weeks of data may be unrepresentative of untagged fish.…”

Cardiac activity in walleye (Sander vitreus) during exposure to and recovery from chemical anaesthesia, electroanaesthesia and electrostunning

“…The heart is innervated by the sympathetic branch of the autonomic nervous system (Sandblom & Axelsson, 2011), which is also implicated in catecholamine release at the beginning of the stress response (Reid et al, 1998), and heart rate can increase rapidly in response to handling and other disturbances (Sopinka et al, 2016). In trial 1, natural circadian rhythms began to appear beneath the recovery trends between the 1-and 2-day marks (Figure 2), corresponding approximately with the mean recovery times which (based on our criteria) ranged from c. 29.4 to 33.5 h. The masking of circadian rhythms normally visible in ECGs can occur following elevated heart rate (see Brijs et al, 2018), though this is not always the case (Føre et al, 2021). Similar fluctuations appeared near the end of each half of trial 2 however these were less consistent than those seen in trial 1.…”

“…In trial 1, natural circadian rhythms began to appear beneath the recovery trends between the 1‐ and 2‐day marks (Figure 2), corresponding approximately with the mean recovery times which (based on our criteria) ranged from c . 29.4 to 33.5 h. The masking of circadian rhythms normally visible in ECGs can occur following elevated heart rate (see Brijs et al , 2018), though this is not always the case (Føre et al , 2021). Similar fluctuations appeared near the end of each half of trial 2 however these were less consistent than those seen in trial 1.…”

“…GAMs. Although recovery is often quantified and analysed in different manners, other experiments investigating heart rates following handling stress (focusing on salmonids) have reported recovery times and visible circadian rhythms over similar timescales, e.g., c. 4 days for Atlantic salmon Salmo salar L. at c. 4-5 C (Føre et al, 2021), and 3+ days for rainbow trout (Oncorhynchus mykiss Walbaum 1792) at c.…”

Sentinels in Salmon Aquaculture: Heart Rates Across Seasons and During Crowding Events

“…Fish recovery in terms of normalized heart rate pattern after tagging can range from days to weeks in tank trials (Hvas et al, 2020b;Føre et al, 2021;Zrini and Gamperl, 2021), and a regular diurnal heart rate cycle is often described as an indicator of a normal fish behavior and hence used as a sign fish have recovered from a tagging procedure (e.g., Brijs et al, 2019b;Føre et al, 2021). However, there is often a concern that the process of adding a tag, or the tag itself, will alter a fish's physiology so that it is no longer representative of untagged fish (Cooke et al, 2011;Jepsen et al, 2015;Macaulay et al, 2021).…”